Field of the Invention
The present invention relates to an image processing apparatus which corrects a deterioration of an image caused by an optical system.
Description of the Related Art
For an object captured via an image pickup optical system, light emitted from one point cannot be converged to another point and has a minute spread due to an influence of a diffraction, an aberration, or the like that occurs in the image pickup optical system. Such a minutely-spread distribution is referred to as a PSF (point spread function). Due to the influence of the image pickup optical system, the captured image is formed with the PSF convolved with the image, and accordingly, the image is blurred and its resolution is deteriorated.
Recently, the captured image is typically stored as electronic data, and a method (image restoration processing) has been proposed which corrects an image deterioration caused by the image pickup optical system by performing image processing. The deterioration state of the image varies depending on a position in an image.
Japanese Patent Laid-open No. 2013-25473 discloses an image processing method for reducing a calculation amount while performing optimum restoration processing depending on a deterioration state at each position even when the deterioration of an image varies depending on a position in the image due to a characteristic of a lens. The literature “OSA VOLUME 62, NUMBER 1 Jan. 1972 Bayesian-Based Iterative Method of Image Restoration” discloses an image restoration method using so-called Lucy-Richardson method (LR method) based on Bayes' theorem.
However, in the image processing method disclosed in Japanese Patent Laid-open No. 2013-25473, the measured PSF is converted into each of vertical and horizontal dispersion values, and accordingly it cannot perform correction for asymmetric deterioration characteristics such as a large coma aberration in principle. The method of using the vertical and horizontal dispersion values of the PSF cannot be applied to a lens-interchangeable camera which has a number of combinations of an optical system and an image pickup element because a unit of a coordinate varies. Especially, in conventional methods of using a lens-interchangeable digital camera which has combinations of various lenses and image pickup elements, a shift-variant deterioration characteristic in a captured image cannot be satisfactorily restored.